1. Field of the Invention
The present invention relates to a projection type image display apparatus for projecting onto a screen under magnification an image displayed in a reflection type liquid crystal display device; and, more specifically, to a projection type image display apparatus using a reflection type liquid crystal display device, which makes illumination light incident on a rectangular reflection type liquid crystal display device by way of a polarization beam splitter.
2. Description of the Prior Art
In recent years, as liquid crystal display devices of projection type image display apparatus, those of reflection type have come into use, since they can attain a higher aperture ratio than those of transmission type, thereby being able to satisfy demands for higher resolution and higher illumination. The reflection type liquid crystal display devices are characterized in that they utilize an optical rotation effect of a liquid crystal, so as to distinguish ON and OFF states of a pixel from each other according to the direction of optical rotation.
Recently, on the other hand, ferroelectric liquid crystal display devices (hereinafter referred to as xe2x80x9cFLC devicesxe2x80x9d), which are a kind of reflection type liquid crystal display devices, have become known. The FLC devices not only have the above-mentioned characteristic features of common reflection type liquid crystal display devices, but also are most characterized in their fast response to voltage applications. When an FLC device exhibiting such a fast response speed is used, a single color wheel can carry out color decomposition in a time series, whereas a conventional transmission type liquid crystal or reflection type liquid crystal uses three devices corresponding to respective primary colors of light in order to display a color image. Namely, the use of FLC devices is advantageous in terms of cost and weight of apparatus, whereby they are expected to be in wider use in projection type image display apparatus from now on.
In general, when a reflection type liquid crystal display distinguishing ON and OFF states of a pixel from each other according to the direction of optical rotation is used for constructing an projection optical system, a polarization beam splitter (hereinafter referred to as xe2x80x9cPBSxe2x80x9d) is often disposed upstream the reflection type liquid crystal display device, immediately in front of the device in particular.
Using a reflection type liquid crystal display device and a PBS in combination as mentioned above is often problematic in that its finally projected images fail to yield a favorable contrast. When a screen is displayed totally black on the liquid crystal display device, all the luminous fluxes are ideally blocked by the PBS. In practice, however, the state of polarization of luminous fluxes reflected by the liquid crystal display may change under the influence of distortion and the like existing within the PBS, whereby the light to be totally blocked may leak toward the screen. Thus, even when the screen is displayed black on the liquid crystal display device, light may reach the screen to a certain extent and enhance the luminance on the screen, thereby lowering the contrast of projected images.
The contrast of an image is generated within the PBS in a process during which a luminous flux reflected by the liquid crystal display is emitted toward the screen by way of the PBS. Therefore, the apparatus is desired to have a configuration yielding a shorter optical path within the PBS.
In such an apparatus, the PBS is arranged between the reflection type liquid crystal display device and the final surface of the projection lens, whereby the projection lens is required to have a certain extent of back focus. Securing a long back focus not only makes it difficult to correct distortion and chromatic aberration in magnification, but also is problematic in that the projection lens itself increases its size. When the apparatus is constructed with a PBS having smaller dimensions such that the luminous flux emitted toward the screen by way of the PBS has a shorter optical path within the PBS, the back focus required for the projection lens also becomes shorter, which is desirable for overcoming the above-mentioned problem as well.
In view of such circumstances, it is an object of the present invention to provide a projection type image display apparatus using a reflection type liquid crystal display device which can improve the contrast of a projected image and reduce the size of a projection lens by yielding a configuration which can reduce dimensions of a PBS such that the luminous flux reflected by the reflection type liquid crystal display device shortens its optical path within the PBS in the process of being emitted toward the screen by way of the PBS.
The present invention provides a projection type image display apparatus which makes illumination light from a light source section incident on a rectangular reflection type liquid crystal display device by way of a polarization beam splitter, optically modulates the illumination light in the reflection type liquid crystal display device, and projects thus modulated light through a projection lens by way of the polarization beam splitter;
wherein a plane including an optical axis of the illumination light incident on the polarization beam splitter and an optical axis of the illumination light emitted from the polarization beam splitter toward the projection lens is substantially parallel to a direction in which a shorter side of the reflection type liquid crystal display device extends.
The illumination light incident on the polarization beam splitter may be bent by about 90 degrees by a polarization separating film within the polarization beam splitter so as to be reflected toward the reflection type liquid crystal display device, reflected by the reflection type liquid crystal display device, and then transmitted through the polarization separating film of the polarization beam splitter so as to be emitted toward the projection lens. Alternatively, the illumination light incident on the polarization beam splitter may be transmitted through a polarization separating film within the polarization beam splitter so as to be emitted toward the reflection type liquid crystal display device, reflected by the reflection type liquid crystal display device, and then bent by about 90 degrees by the polarization separating film of the polarization beam splitter so as to be reflected toward the projection lens.
Preferably, the apparatus further comprises color decomposing means for decomposing the illumination light from the light source section into a plurality of color light components.
Preferably, the light source section outputs nonpolarized illumination light, whereas the illumination light is made incident on the polarization beam splitter by way of an integrator section for homogenizing an intensity distribution of the illumination light within a cross section perpendicular to an optical axis thereof and polarization converting means for converting the illumination light into linearly polarized light vibrating in one direction.
The integrator section may comprise a rod integrator.
The integrator section may comprise a flyeye integrator composed of at least two flyeyes, each constituted by a plurality of lenses arranged two-dimensionally, disposed on an optical axis, whereas a polarization converting device may be disposed as the polarization converting means downstream the integrator section, the polarization converting device comprising a beam splitter for splitting the incident nonpolarized illumination light into first and second polarized light beams having respective polarized light components orthogonal to each other, a mirror for reflecting one of the polarized light beams separated by the beam splitter, and a phase plate for turning one of the polarized light beams into a light beam having the same direction of polarization as that of the other polarized light beam, so that the nonpolarized illumination light is emitted after being converted into light having only one of the polarized light components.
Preferably, the color decomposing means is a color wheel apparatus or color switching device.
The light source section may output substantially parallel illumination light, whereas the illumination light may be made incident on the integrator section by way of an afocal unit comprising front- and rear-group lenses constituting a substantially afocal system and a transmission type color wheel disposed as the color decomposing means near a focal point of the afocal system.
The front- and rear-group lenses of the afocal unit may be constituted by components identical to each other.
The front-group lens of the afocal unit or the afocal unit as a whole may be made detachable.
Preferably, the reflection type liquid crystal display device is a ferroelectric liquid crystal display device.
Preferably, the illumination light is made incident on the polarization separating film of the polarization beam splitter as S-polarized light and then bent by about 90 degrees by the polarization separating film so as to be reflected toward the reflection type liquid crystal display device, or is made incident on the polarization separating film of the polarization beam splitter as P-polarized light and then transmitted through the polarization separating film so as to be emitted toward the reflection type liquid crystal display device.
At least one optical component disposed in an optical path from the light source section to the reflection type liquid crystal display device may have an aspheric form.